Automatic burner control system



Aug. 58, 1944.

F. E. LANGE AUTOMATIC BURNER CONTROL SYSTEM Filed July l0, 1941 2 SheetS-Sheet 1 Fig. 2.

{NVNTOR rcaridi. T.. Beluga.

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ATTQSRNEY Aug. 8, 194151:s E. www:

AUTOMTG BURNER CONTROL SYSTEM ATTRNEY Patented Aug. 8, 1944 AUTOMATIC BURNER CONTROL SYSTEM Frederick E. Lange, Lincoln, Nebr., assignor to Minneapolis-Honeywell Regulator (kmpany, Minneapolis, Minn., a corporation of Delaware Application July 10, 1941, Serial No. 401,736

19 Claims.

This invention relates generally to the automatic control of electrical devices for delivering fuel to a burner, and more specifically to burner motor control systems in which provision is made for locking out the burner motor upon failurev tecting the presence or absence of combustion,

and the second, a safety switch in the form of an electrically heated, thermally operated time switch which deenergizes and locks out the burner motor in the event that its heater is not deenergized rst by said combustion responsive device in response to the establishment of combustion.

One of the principal objects of the present invention is to combine the functions of the combustion responsive device and safety switch into one instrument.

Another object is to provide a fluid fuel burner system with a thermal device which is electrically heated in response to a demand for burner operation for energizing the burner motor, and is then heated directly by the heat of combustion to maintain burner operation. Still another object is to utilize this same thermal device for deenergizing the burner motor and locking it out in the event that combustion is not established, or upon a subsequent failure of combustion.

A further object of the invention is to provide the above system withV a means to interpose a predetermined -minimum time delay between successive ener'gzations of the burner motor.

These andother objects will be readily apparent asthe following specification is read in the lightof the accompanying drawings in which Figure l"-shows schematically a fuel burner control vv'system embodying the various features of my present invention,

y Figure 2 is a schematic showing of a modification of my invention, and

Figure 3 shows schematically a third form of my invention.

Referring now to Figure l, the reference numeral I indicates an elongated expansible metal ribbon formed of two legs II and I2. The metal ribbon I0 is stretched across a tensioning member I3fand the two extremities of the ribbon are connected to the supporting members I4 and I5. A spring I6 carries the lower end of the tensioning member I3 and exerts a force upwardly so that this member lI3 yapplies a tension to the ribbon III. The upper end of the member I3 is in the form of a contact arm I1 which is adapted to move between a cold contact C and a hot contact H.

The device is so adjusted that expansion of o'ne of the two legs with respect to the other will cause a movement of the contact arm I1 by reason of the fact that the tensioning member I3 will rotate about the point I8 at which it is supported by the bowed spring I6. For example, if the leg II were heated to a temperature above that of the leg I2 then the leg II would expand and cause the tensioning member I3 to rotate in a clockwise direction about the Ipoint I8 and the contact arm I1 would thereupon move toward the right as seen in Figure 1.

The device Ill is so adjusted that when the two legs I I and I2 are at the same temperature, the contact arm I1 will be in engagement with the cold contact C, and when the leg II is heated to a temperature above that of leg I2, the resultant expansion of leg II causes the contact arm I I to move over into engagement with the contact H.

It will be appreciated that the operation of the switches C and H is entirely independent of the actual temperatureof the two legs II and I2. The operation of these switches depends only upon a differential in Atemperature existing between these two legs.

An electric heater 20 is mounted on the leg I I for the purpose of heating the same. Electric heater 2| is mounted upon the leg I2 for the same purpose. The heater 2I however is provided with a suitable lagging 22 so that the heat developed by the heater 2I will be delayed in reaching the leg I2 whereas the heat from the electric heater 20 will be immediately transmitted to leg I I. The result of this arrangement is that when the two heaters 20 and 2I are simultaneously energized the leg II will heat more rapidly than the leg I2, but after a predetermined time interval these legs will reach the same temperature. The'effect on the contact arm I1 is that upon energization of the two heaters 20 and 2|, the leg II will first be heated to a temperature above that of leg I2 and the arm I'I will ilrst be rotated toward the right as seen in Figure 1, and then as the two legs reach the same temperature contact arm I1 will rotate toward the left and return to its original position.

The contacts C and H and the contact arm I1 are shown diagrammatically. Actually this switching arrangement operates to close a circuit from the contact arrn l1 to the hot contact H before the circuit is broken between thel cold contact C and the contact arm I1. Thus as the contact arm I1 moves toward the right as seen in Figure l, the control of these circuits overlap. As the contact arm I1 moves toward the leftl it will first break the circuit-between the hot contact H and the contact arm I1 and later make the circuit between the cold contact C and the contact arm I1. To state it diiferently, the hot contact is always actuated before the cold contact so that it makes first on movement of the arm I1 to the right and breaks first on movement of this arm to the left. This switch function is well known in the prior art and there are a great many patented devices for accomplishing it. Further description thereof is therefore believed unnecessary.

The furnace wall 9 is provided with an opening in which a tube 25 is located. This tube, only a portion of which is shown in the drawings, serves to direct radiant heat from the name produced by the burner onto the leg II of the thermal device I whereby this leg may be heated during the period that combustion is present within the furnace. The leg I2 is protected so that radiant heat from the furnace cannot strike it, and therefore during the period that combustion is present within the furnace the leg II will be maintained at a higher temperature than the leg I2, and the contact arm I1 will therefore remain in engagement with the hot contact H. This will be true regardless of the energizatlon of the two electric heaters and 2 I,

Located in the room, or other region where the temperature is to be controlled, is a thermostat in the form of a bimetal coil 26. This coil is fixed at one end and at the other end carries a con` tact blade 21 which on a decrease in temperature is moved by the coil 26 into engagement with the stationary contact 28. A permanent magnet 23 may be provided for the purpose of assuring positive action between the blade 21 and the contact 28.

A relay winding 30 is adapted when energized to attract its armature, indicated by the dotted line 3l, which simultaneously moves the contact arm 32 into engagement with the stationary contact 33 and the contact arm 34 into engagement with the stationary contact 36. A relatively high resistance 36 is located in series with the contact 33 for a purpose to be later described.

The reference numeral 31 indicates an electrical device for controlling the flow of fuel to the burner and an electrical ignition device for the fuel is indicated at 36. Obviously any other type of ignition means may be substituted therefor, such as a constantly burning gas pilot flame, for example. For the purpose of this description, the system will be referred to as an oil burner control system, and therefore the electrical device 31 will be the conventional type of oil burner motor. The electrical energy for operating the system is supplied by means of the two line wires 39 and 40.

A manually operated switch is provided for deenergizing the heater for a predetermined period of time. This switch comprises a push button actuated switch plate 63 associated with a dashpot 62. The dash-pot 62 includes a cylinder 64 in which a piston 65 operates. A' spring 66 serves to bias the piston in switch closing direction. The dash-pot 62 is of any conventional type in which the movement in one direction only is irnpeded. Thus, the operator is able to quickly open the switch by moving the switch plate 63 away from the switch contacts. After the Switch 1S 7l thus opened, the switch is slowly returned to closed position by a spring 66 under the control of dash-pot 62.

Operation The system has been shown in its satisfied position in which the thermostat 26 has separated the contact blade 21 from the contact 26. The burner motor 31 is deenergized as well as the two electrical heaters 20 and 2| and the thermal device Il) is therefore in its cold position at which time the contact arm I1 engages the cold contact C and is disengaged from the hot contact H. This is because the two legs II and I2 of the thermal device YII) have reached the same' temperature, there being no heat applied to them by the heaters or by the furnace combustion chamber.

Due to the fact that the burner motor 31 is deenergized, the temperature in the space in which the thermostat 26 is located will begin to fall, and when it reaches a predetermined value the thermostat 26 will cause the contact blade 21 to engage the stationary contact 28. This will establish a circuit from line wire 33 through conductor 42, relay winding 30, conductor 43, thermostat 26, contact blade 21, stationary contact 26. conductor 44, switch plate 63, conductor 46, electric heater 2|, conductor 46, electric heater 20, conductor 41, cold contact C, contact arm I1 and conductor 48 back to the other line wire 40. The above circuit results in the simultaneous energization of the two electric heaters 20 and 2|, with the result that the leg I I will be immediately heated to a temperature above that of the leg I2. This will cause a rotation of the tensioning member I3 and the contact arm I1 will then close a circuit with the hot contact H. It will be noted that the relay winding 30 was energized at the same time as the two electric heaters 2Il and 2| with the result that the two arms 32 and 34 will move into engagement with the contacts 33 and 35 respectively. No new circuits are established by the energization of the relay, but when contact arm I1 engages the hot contact H a circuit is set up in parallel with the two electric heaters 2B and 2l. This circuit extends from the conductor 44 through switch plate 63, conductor 50, resistance 36, conductor 5I, contact 33, switch arm 32, conductor 52, conductor 53, hot contact H, and contact arm I1 to conductor 46. The relatively high electrical resistance 36, which is now in parallel with the electric heaters 20 and 2 I, prevents these heaters from being deenergized.

When the contact arm I1 engages the hot'contact H an energizing circuit for the burner motor and ignition device is also established from supply line 39 through conductor 56, then through one circuit comprising conductor 56, burner motor 31 and conductor 51 and through a parallel circuit comprising conductor 66, electrical ignition device 38 and conductor 53. From the Junction of the conductors 51 and 63 the circuit continues through conductor 60, contact 36, switch arm 34, conductor 53, hot contact H, contact arm I1 and conductor 46 back to the other line wire 43.

Let it be assumed rst that for some reason the energization of the burner motor 31 and ignition device 38 does not result in the" combustion of fuel at the burner. There will therefore be no name and hence no radiant heat will irnplnge upon the leg II of the thermal device I6.v A predetermined time after the switcharm I1 has been moved into engagement with the hot contact H (usually about seconds) the lagged heater 2| Will cause the leg I2 to come up to about the same temperature as the leg II at which time the con,-

tact arm I1 will disengage thel hot contact H which will resultl in the deenergization of the burner motor and ignition device. Preferably the resistance values of the heaters 20 and 2| are so chosen that upon energization the leg II will be expanded sufficiently to close the hot switch H but insuillcient to open-the cold switch C. In

this way the heaters will remain continuously energized during the trial ignition period. As the thermostat 28 is still calling for heat, the heaters 20 and 2| will remain energized, thereby eii'ectively locking the system in a condition where the burner motor cannot be reenergized until manual intervention occurs. This manual intervention consists of opening the manual switch 63. The delayedreclosure oi' the switch due to the action of dash-pot 62 is suillcient to allow both legs I I and I2 to cool down to such an extent that upon reenergization of thesev two heaters 20 and 2|, the leg II will be heated to a value above that of leg I2 causing the contact I1 to again engage the hot contact H to reenergize the burner motor 31.

Let it be assumed now that the two electric heaters 20 and 2| have been energized and the contact arm I1. has engaged the hot contact H and energized the burner motor 31 and the electric ignition device 38 and that as a result combustion has been established in the combustion chamber of the furnace. Radiant heat from the flame produced will now impinge directly upon the leg II and keep this leg at a temperature above that of the leg I2 even though at this time the electric heaters 20 and 2| remain energized. As a matter of fact the effect of the radiant heat on theleg II is such that the expansion of this leg is increased to suchan extent that the arm |1 disengages the cold contact C and deenergizes the two electric heaters 20 and 2|. Therefore at this time the hot contact H remains closed due directly to the eiect of the radiant heat from the ame on the thermal device I0. This is the running condition' of the system.

In the event of a flame failure the leg II will cool and contract and the arm I1 will immediately open the hot contact H and deenergize the burner motor. After a predetermined interval of time the two legs will reach the same temperature and the cold contact C will be closed, thereby reestablishing the original energizing circuit through the two heaters 20 and 2| and the system will again attempt to start. If thedifiiculty has been corrected and combustion is established, the system will attain its running condition as before.`

Otherwise it will lock itself out as described above.

A power failure will deenergize the burner mov tor and the thermal device I0 will open the hot SYSTEM oF FIGURE 2 The system disclosed in Figure 2 is somewhat different from that disclosed in Figure 1 in that in Figure 2 the contact arm I1 closes a hot contact H, the same as in Figure 1, but there is no cold contact C in this modification. The thermal device I is an exact duplicate of the thermal device I0 of Figure 1 and is provided with the same fast heater 20 and lagged heater 2|. In this modification, the contact arm 1 may be provided with a permanent magnet IIO in order to assure a positive contact action between the contact arm I1 and hot contact H. l

The relay winding III in this case, when energized, moves a contact arm |I2 into engagement with the stationary contact I I3. This movement is retarded by means of a dash-pot indicated generally at III and similar to the dash-pot 62 of Figure 1. 'Ihe dash-pot |I4 is provided with a piston ||5 which retards the movement of the contact |I2 to closed position upon the energization of the 'winding III but which permits the immediate operation of the contact arm |I2 and contact I|3 upon the deenergization of the winding III. Such devices` are well known commercially and no further description is believed necessary.

The reference numeral I 0I indicates a manually operable switch having a switch plate |02 for breaking the circuit.

Operation Upon a call for heat by the thermostat 26, a circuit is established from the line wire 39 through conductor ||6, thermostat 2B, contact blade 21, stationary contact ||1, conductor 8, relay winding IH, conductor H9, switch plate |02, and conductor |04 back to the other line wire 40. This circuit energizes the relay winding I I and after a predetermined interval of time, determined by the timing of the dash-pot II4, the contact arm ||2 engages the stationary Contact ||3. This establishes the following circuit: from line wire 39 through conductor |20, stationary contact |I3, contact arm II2, conductors I2| and |22, lagged heater 2|, conductor |23, fast heater 20 and conductor |24 back to the other line wire 40. The establishment of this c'i'cuit results in the heater 20 heating the leg II to a temperature above that of leg I2 so that the contact arm I1 will engage the hot contact H. The closureof this contact establishes a circuit from line Wire 39 through conductor |20, contact II3, contact arm |I2, conductors I2I and |26, contact H, contact arm I1, conductors |21 and |28, burner motor 3'l'and conductor |29-I30 back to the other line wire 40. Conductors |3I and |32 connect the electrical ignition device 38 in parallel with the burner motor 31.

If combustion is not established at thisv time the legs II and I2 of the thermal device I0 will soon reach the same temperature and the arm I1 will therefore disengage the hot contact H and the burner motor will be locked in deenergized position in the same manner as in Figure l. In order to reset the system for operation at this time, it is only necessary to momentarily deener gize the winding ||I by openingswitch IOI. This will immediately open the switch II2-I I3 and the dash-pot I|4 is desgned to interpose a sufcient delay in the closing of this switch to per' mit the two legs and I2 to cool suiliciently. Upon reenergization of the heaters 20 and 2| the arm I1 will reenergize the burner motor and ignition device by closing against the hot contact H.

If combustion is successfully established the leg I I will be maintained in engagement with the hot contact H due to the radiant heat from the combustion chamber 25. 4In this modification the two heaters 20 and 2| will remain energized but the effect of the radiant heat on the leg II is sufficient to maintain the hot contact closed.

On a momentary power failure the switch |I2-II3 will be immediately opened and the dash-pot I|4 will insure a proper delay in the reclosing of the circuit.

SYSTEM or FIGURE 3 The modification disclosed in Figure 3 is the same as that disclosed in Figure 2 except that a thermal time delay means has been substituted for the dash-pot I|4 of Figure 2. In this modication, the relay winding 21| when energized moves the contact arm 2|2 into engagement with the stationary contact 2|3 and when deenergized the contact arm 2|2 engages contact 2I4. The time delay is provided by means of a bimetal thermostat 2|5 which is heated by means of an electrical heater 2|6. The thermostat 2 I5 carries a movable contact 2 I1 which in the cold position of the thermostat engages Contact C and in its hot position engages contact H. A permanent magnet 2I8 is provided for causing the contact to move with a snap action between contacts C and H.

The thermal device I and its switch action are exactly the same as in Figure 2 and will not be described again. Similarly, the manual switch |0| is the same as in Figure 2.

Operation On a call for heat by the thermostat 26, a circuit is established from line wire 39 through conductor 220, thermostat 26, contact blade 21, contact 22|, conductor 222, switch plate |02, conductor 223, contact arm 2|2, contact 2|4, conductor 224, electric heater 2|6 and conductors 225 and 226 back to the other line wire 40. This results in the heating of the bimetal 2|5, and when it attains a predetermined temperature it will snap the movable contact 2|1 from engagement with the cold contact C to engagement with the hot contact H. This will establish a circuit from the line wire 39 through conductor 220, thermostat 26, contact blade 21, contact 22 I conductor 222, switch plate |02, conductor 228, contact H, movable contact 2|1, bimetal 2|5, cony ductors 226 and 230, relay winding 2|| and conductor 226 back to the other line wire 40. Upon energization of the relay winding 2| I, the relay arm 2I2 will separate from contact 2|4 and engage contact 2 I 3. This breaks the circuit through the heater 2|6 of the bimetal 2I5 and sets up a holding circuit for the relay winding 2|| which is independent of the hot contact H. This holding circuit may be traced from line wire 39, conductor 220, thermostat 26, contact blade 21, contact 22|, conductor 222, switch plate |02, conductor 223, relay arm 2|2, contact 2|3, conductors 23| and 230, relay winding 2| I and conductor 226 back to the other line wire 40. After a predetermined time interval the bimetal 2 I 5 will cool sufficiently to snap the contact 2|1 out of engagement with the contact H and into engagement with the contact C. This results in the establishment of an energizing circuit for the two heaters 20 and 2| for the two legs II and I2 respectively of the thermal device I0. This circuit extends from the line wire 39 through conductor 220, thermostat 26, contact blade 21, contact 22|, conductor 222, switch plate |02, conductor 223, relay arm 2|2, contact 2I3, conductors 23| and 229, bimetal 2|5, contact 2|1, contact C, conductors 235 and 236, lagged heater 2|, conductor 231, fast heater 20 and conductor 236 back to the tors 24| and 242, burner motor 31 and conductors 243 and 244 to line wire 40. The conductors 245 and 246 connect the ignition device 38 in parallel with the burner motor 31.

If combustion is not established the system is locked out the same as in the other two modifications, whereas if combustion is established the radiant heat from the combustion chamber 25 heats the leg II and maintains the hot contact H closed.

On a power failure or upon satisfaction of the thermostat 26, the relay winding 2|| will be deenergized and the contact arm 2I2 will separate from contact 2|3 and engage the contact 2|4. This results in the deenergization of the two heaters 20 and 2| and also of the burner motor 31 and ignition device 36. The two heaters 20 and 2| cannot now be reenergized until the heater 2|6 is reenergized to cause the bimetal 2|5 to move the contact 2 I1 into engagement with contact H which energizes the relay 2 II and breaks the circuit to the heater 2 I 6 and until the bimetal 2 I 5 subsequently cools and causes the contact 2|1 to separate from contact H and engage the contact C. This time delay gives the two legs II and I2 of the thermal device suillcient time to cool so that upon reenergization of the two heaters 20 and 2| the contact arm I1 will again be moved into engagement with the contact H.

In order to manually reset this system for operation following a lock out due to failure of combustion, it is necessary only that the circuit to the relay winding 2|| be momentarily broken. This may be accomplished by momentarily opening switch |0I.

It will therefore be seen that I have provided an improved fuel burner control system in which the functions of the safety switch and the combustion responsive thermostat have been combined into one instrument which is my thermal device I0. This thermal device I0 acts to deenergize and lock out the burner motor in the event of an original failure of ignition and also directly detects the establishment of combustion to maintain burner operation in the event that combustion is established before the system is locked out. 'I'he three modifications have been disclosed merely for the purposes of illustration, and as many additional modifications falling within the scope of this invention will occur to those who are skilled in the art I intend to be limited only by the appended claims.

I claim as my invention:

1. An automatic fuel burner control system comprising in combination, an electrical device for controlling the ow of fuel to said burner, means for igniting said fuel, control means for said device including a thermal means having two heat sensitive portions which, when they are both at substantially the same temperature, cause said control means to assume a predetermined position in which said electrical device is deenergized, means operated in response to a demand for burner operation for heating one of said portions rapidly and the other portion slowly whereby said control means is moved in one direction toenergize said electrical device for a predetermined period of time and then return to its original position, and means for additionally heating said one portion upon the establishment of combustion to prevent the control means from returning to its original position.

2. An automatic fuel burner control system comprising in combination, an electrical device -for controlling the flow of fuel to said burner,

means for igniting said fuel, control means for said device including a thermal means having two heat sensitive portions which, when they are both at substantially the same temperature, cause said control means to assume a predetermined position in which said electrical device is deenergized, means operated in response to a demand for burner operation for heating one of said portions rapidly and the other portion slowly whereby said control means is moved in one direction to energize said electrical device for a predetermined period of time and then returns to its original position, said one portion being so located as to respond tothe heat of combustion and prevent the return of said control means to its original position if combustion is established first.

3. An automatic fuel burner control system comprising in combination, an electrical device for controlling the ow of fuel to said burner, means for igniting said fuel, control means for said device including a thermal means having two heat sensitive portions which, when they are both at substantially the same temperature, cause said control means to assume a predetermined position in which said electrical device is deenergized, means operated in response to a demand for burner operation for heating one of said portions rapidly and the other portion slowly whereby said control means is moved in one direction to energizesaid electrical device for a predetermined period of time and then returns to its original position, said one portion being so located as to respond to the heat of combustion and prevent the return of said control means to its original position if combustion is established first, said one portion causing the return of said control means to its original position upon a subsequent failure of combustion, and means interposing a delay between successive energizations of said electrical device.

4. An automatic fuel burner control system comprising in combination, an electrical device for controlling the ow of fuel to said burner, means for igniting said fuel, control means for said device including a thermal means having two heat sensitive portions which, when they are both at substantially the same temperature, cause said control means to assume a predetermined position in which said electrical vdevice is deenergized,

means operated in response to a demand for burner operation for heating one of said portions rapidly and the other portion slowly whereby said control means is moved in one direction to energize said electrical device for a predetermined period of time and then returns to its original position, means for additionally-heating said one portion upon the establishment of combustion to prevent the control means from. returning to its original position, and means for manually deenergizing said heating means in the event of a failure of combustion whereby the system ls reset for another starting attempt.

5. An, automatic fuel burner control system comprising in combination, an electrical device controlling the flow of fuel to said burner, means for igniting thefuel, a cold switch, a hot switch, thermal means having two heat sensitive portions, said thermal means closing said cold switch when both of said portions are at substantially the same temperature and closing said hot switch when one of said portions is heated above the other, a quick acting electrical heater for said one portion, a slow acting electrical heater for said other portion, a main switch, a circuit for said heaters including said main switch and cold switch, a circuit for said electrical device including said hot switch, and means additionally heating said one portion upon the establishment of combustion.

, 6. An automatic fuel burner control system comprising in combination, an electrical device controlling the flow of fuel to said burner, means for igniting the fuel, a cold switch, a hot switch, thermal means having two heat sensitive portions, said thermal means closing said cold switch when both of said portions are at substantially the same temperature and closing said hot switch when one of said portions is heated above the other, a quick acting electrical heater for said one portion, a slow acting electrical heater for said other portion, a main switch, a circuit for said heaters including said main switch and cold switch, a circuit for said electrical device including said hot switch, said one portion being so located as to respond to combustion in a manner to keep said hot switch closed.

7. An automatic fuel burner control system comprising in combination, an electrical device controlling the flow of fuel to said burner, means for igniting the fuel, a cold switch, a hot switch, thermal means having two heat sensitive portions, said thermal means closing said cold switch when -both of said portions are at substantially the same temperature and closing said hot switch when one of said portions is heated above the other, a 'quick acting electrical heater for said one portion, a slow acting electrical heater for said other portion, a main switch, a circuit for said heaters including said main switch and cold switch, a circuit for said electrical device including said hot switch, said hot switch closing before the cold switch opens on movement of said thermal means in one direction and opening before said cold switch closes on movement of said thermal means in the opposite direction, said one portion being so located as to respond to combustion in a manner to keep' said hot switch closed.

8. vAn automatic fuel burner control system comprising in combination, an electrical device controlling the flow of fuel to said burner, means for igniting the fuel, a. cold switch, a hot switch, thermal means having two heat sensitive portions, said thermal means closing said cold switch when both of said portions are at substantially the same temperature and closing said hot switch when one of said portions is heated above the other, a quick acting electrical heater for said one portion, a slow acting electrical heater for said other portion, a main switch, a relay winding, a rst circuit including said main switch, relay winding, both electrical heaters, and said cold switch, a switch closed by said relaywinding, a circuit for said electrical device including said relay switch and hot switch, and means providing for the additional heating of said one portion upon the establishment of combustion.

9. An automatic fuel burner control system comprising in combination, an electrical device controlling the now of fuel to said burner, means for igniting the fuel, a cold switch, a hot switch, thermal means having two heat sensitive portions, said thermal means closing said cold switch when both of said portions are at substantially the same temperature and closing said hot switch when one of said portions is heated above the other, a quick acting electrical heater for said one portion, a slow acting electrical heater for said other portion, a main switch, a relay winding, a first circuit including said main switch, relay winding, both electrical heaters, and said cold switch, a switch closed by said relay winding, a circuit for said electrical device including said relay switch and hot switch, means providing for the additional heating of said one portion upon the establishment of combustion, and means interposing a delay before the cold switch is closed following the extinguishment of the burner whereby a predetermined minimum time interval must elapse between successive energizations of said electrical device.

10. An automatic fuel burner control system comprising in combination, an electrical device controlling the ow of fuel to said burner, means for igniting the fuel, a cold switch, a hot switch, thermal means having two heat sensitive portions, said thermal means closing said cold switch when both of said portions are at substantially the same temperature and closing said hot switch when one of said portions is heated above the other, a quick acting electrical heater for said one portion, a slow acting electrical heater for said other portion, a main switch, a relay winding, a first circuit including said main switch, relay winding, both electrical heaters, and said cold switch, a switch closed by said relay winding, a circuit for said electrical device including said relay switch and hot switch, a second switch closed by said relay winding, a holding circuit for said relay winding including said main switch, second switch, and hot switch, and means providing for the additional heating of said one portion upon the establishment of combustion for maintaining said hot switch closed as long as combustion exists.

11. An automatic fuel burner control system comprising in combination, an electrical device controlling the flow of fuel to said burner, means for igniting the fuel, a cold switch, a hot switch, thermal means having two heat sensitive portions, said thermal means closing said cold switch when both of said portions are at substantially the same temperature and closing said hot switch when one of said portions is heated above the other, a quick acting electrical heater for said one portion, a slow acting electrical heater for said other portion, a main switch, a relay winding, a first circuit including said main switch, relay winding, both electrical heaters, and said cold switch, a switch closed by said relay winding, a circuit for said electrical device including said relay switch and hot switch, a second switch closed by said relay, a shunt circuit around said two heaters, said shunt circuit including said main switch, said second switch, and said hot switch, a resistance element in said shunt circuit to prevent the short circuiting of said electrical heaters when both of said hot and cold switches are closed, and means providing for the additional heating of said one portion upon the establishment of combustion for maintaining said hot switch closed as long as combustion exists.

12. An automatic fuel burner control system comprising in combination, an electrical device controlling the flow of fuel to the burner, means for igniting the fuel, a hot switch, thermal means having two heat sensitive portions, said thermal means opening said hot switch when both of said portions are at substantially the same temperature and closing said hot switch when one of said portions is heated up above the other, a quick acting electrical heater for said one portion and a slow acting electrical heater for said other portion, circuit closing means operating in response to a demand for burner operation for closing a circuit through said two electrical heaters, a circuit for said electrical device including said hot switch, means providing for the additional heating of said one portion upon the establishment of combustion whereby said thermal means maintains said hot switch closed, and means for breaking the circuit to said electrical device when the demand for burner operation ceases.

13. An automatic fuel burner control system comprising in combination, an electrical device controlling the flow of fuel to the burner, means for igniting the fuel, a. hot switch, thermal means having two heat sensitive portions, said thermal means opening said hot switch when both of said portions are at substantially the same temperature and closing said hot switch when one of said portions is heated up above the other, a quick acting electrical heater for said one portion and a slow acting electrical heater for said other portion, circuit closing means operating in response to a demand for burner operation for closing a circuit through said two electrical heaters, a circuit for said electrical device including said hot switch, and said circuit closing means, means providing for the additional heating of said one portion upon the establishment of combustion whereby said thermal means maintains said hot switch closed, and means retarding the action of said circuit closing means for interposing a predetermined time delay between successive energizations of said electrical device.

14. An automatic fuel burner control system comprising in combination, an electrical device controlling the ow of fuel to the burner, means for igniting the fuel, a hot switch, thermal means having two heat sensitive portions, said thermal means opening said hot switch when both of said portions are at substantially the same temperature and closing said hot switch when one of said portions is heated up above the other, a quick acting electrical heater for said one portion and a slow acting electrical heater for said other portion, a main switch, a relay winding for closing said main switch, means delaying the closure of said main switch following the energization of said winding but permitting said switch to open immediately upon deenergization of said winding, means for energizing said winding in response to a. demand for burner operation, a circuit for said two electrical heaters including said main switch, a circuit for said electrical device including said main switch and said hot switch, and means providing for the additional heating of said one portion upon the establishment of combustion whereby said thermal means maintains said hot switch closed.

15. An automatic fuel burner control system comprising in combination, an electrical device controlling the flow of fuel to the burn fr, means for igniting the fuel, a hot switch, thermal means having two heat sensitive portions, said thermal means opening said hot switch when both of said portions are at substantially the same temperature and closing said hot switch when one of said portions is heated up above the other, a quick acting electrical heater for said one portion and a slow acting electrical heater for said other portion, a main switch, a relay winding for closing said main switch, means delaying the closure of said main switch following the energization of said winding but permitting said switch to open immediately upon deenergization of said winding, means for energizing said winding in response to a demand for burner operation, a circuit for said two electric heaters including said main switch, a circuit for said electrical device including said main switch and said hot switch, means providing for the additional heating of said one portion upon the establishment of combustion whereby said thermal means maintains said hot switch closed, and a manual switch in circuit with said relay winding for reconditioning ythe system for operation following a failure of combustion during a demand for burner operation.

16. In a burner control device, a ribbon of a material expansible with temperature, a pivoted switchA actuating arm, means for placing said ribbon under tension with an intermediate point thereofA engaging said switch actuating arm so that said switch actuating member assumes a position dependent upon the relative expansion of the two portions of the ribbon on opposite sides of said intermediate point, an electrical 1 heater for heating one portion of said ribbon suillciently to tend to cause movement of said switch actuating arm in one direction away from a predetermined position, means for heating the i other portion in response to the establishment of combustion to cause said switch actuating arm to remain in said predetermined position, and a burner control switch associated with said switch actuating arm and held in' closed position when said switch actuating arm is in said predetermined position.

17. In a burner control device, a ribbon of a material expansible with temperature, a pivoted switch actuating arm, means for placing said ribbon under tension with an intermediate point thereof engaging said switch actuating arm so that said switch actuating member assumes a position dependent upon the relative expansion of the two portions of the ribbon on opposite sides of said intermediate point, an electrical heater for heating one portion of said ribbon sumciently to tend to cause movement of said switch actuating arm in one direction away from a predetermined position, means for heating the other portion in response to the establishment of combustion to cause said switch actuating arm to remain in said predetermined position, a burner control switch associated with said switch actuating arm and held in closed position when said switch actuating arm is in said predetermined position, and relay means for controlling the energizaticn of said heater, said relay means being operative a predetermined period of time after energ'ization thereof to cause energizatlon of said electric heater and operative upon deenergization thereof to cause immediate deenergization of said heater.

18. In a burner control device, a pair of'exy lone -direction from a normal cold position to a predetermined position, a slow acting electrical `heater connected in series with said quick acting heater and associated with the other of said elements to cause movement of said switch actuating member in the opposite -direction away from said predetermined position, means for additionally heating said first .element in response to the establishment of combustion to cause said switch actuating member to remain in said predetermined position despite the action of said slow acting heater, and a burner control switch held in closed position when said switch actuating member is in said predetermined position.

19. An automatic fuel burner control system comprising in combination, an electrical device fortfeeding fuel to said burner, means for igniting the fuel, a control switch for said electrical device, an actuator for said switch, a continuous ribbon member of thermally extensible mono-metallic material, said ribbon member having two portions each adapted to be heated, means including said actuator for operatively connecting the midportion of said ribbon to said switch to maintain said switch-in either a iirst position in which operation of said burner is permitted or a second position depending upon the relative lengths of said two portions as aifected'by theirrelative temperatures, electrical means associated with said member for heating one of said portions so as to tend to cause said member to move said switch from said ilrst to said second position, and means i'or subjecting the other of said portions of said member to the heat of combustion of said burner to cause it to be heated so thatsaid member maintains said switch in said rst position despite said electrical heating means.

- l'RlDlRJCK E. LANGE. 

